Question

我是WPF开发的新手。我刚刚创建了一个示例来重新创建场景。我根据父行中的复选框切换rowdetailsview中datagrid的IsReadonly属性。

除了特定情况外，一切正常。

如何重现问题。

保持最初创建的父行检查。取消选中父行。转到子行id属性。清除id字段中的所有内容并从该单元格中删除选项卡，您将看到空引用异常。

我不知道如何解决这个问题。任何见解都会非常有用。

代码背后的代码：

 namespace WpfApplication7
{/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{

    public PerColl People { get; private set; }
    public MainWindow()
    {
        InitializeComponent();

        this.People = new PerColl();
        this.DataContext = this;
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {

    }

    public class Person
   : INotifyPropertyChanged, IEditableObject
    {
        public string Name { get; set; }

        public double Salary
        {
            get { return _salary; }
            set
            {
                if (this._salary == value)
                    return;
                this._salary = value;
                if (this.PropertyChanged != null)
                    this.PropertyChanged(this, new PropertyChangedEventArgs("Salary"));
            }

        }

        public bool IsLocked
        {
            get { return _isLocked; }
            set
            {

                if (this._isLocked == value)
                    return;
                this._isLocked = value;
                if (this.PropertyChanged != null)
                    this.PropertyChanged(this, new PropertyChangedEventArgs("IsLocked"));
            }
        }

        public ObservableCollection<Kid> Kids { get; set; }

        public Person(string name, double salary)
        {
            this.Name = name;
            this.Salary = salary;
        }


        public Person()
        {
            this.Salary = 10000;
            this.Name = "abc";
            this.IsLocked = true;
            this.Kids = new ObservableCollection<Kid>();
            this.Kids.Add(new Kid(1));
            this.Kids.Add(new Kid(2));
        }

        private bool _isLocked;
        private double _salary;
        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion

        public void BeginEdit()
        {
            if (isEdit) return;
            isEdit = true;
            this.backup = this.MemberwiseClone() as Person;
        }


        public void CancelEdit()
        {
            if (!this.isEdit)
                return;
            isEdit = false;
            this.Name = this.backup.Name;
            this.Salary = this.backup.Salary;
        }

        public void EndEdit()
        {
            if (this.isEdit == false)
                return;
            this.isEdit = false;
            this.backup = null;
        }



        private bool isEdit;
        private Person backup;
    }


    public class PerColl : ObservableCollection<Person> { }

    public class Kid : IEditableObject,INotifyPropertyChanged
    {
        public int Id
        {
            get { return _id; }
            set
            {
                this._id = value;
                if (PropertyChanged != null)
                    this.PropertyChanged(this, new PropertyChangedEventArgs("Id"));

            }

        }
        public string Name
        {
            get { return _name; }
            set
            {
                this._name = value;
                if (PropertyChanged != null)
                    this.PropertyChanged(this, new PropertyChangedEventArgs("Name"));

            }
        }
        public Person Parent { get; set; }

        public Kid()
        {
            this.Id = 12345;
            this.Name = "kidname";
        }

        public Kid(int id, string name = "kidname")
        {
            this.Id = 12345;
            this.Name = name;
        }

        #region IEditableObject Members

        public void BeginEdit()
        {
            if (isEdit) return;
            isEdit = true;
            this.backup = this.MemberwiseClone() as Kid;
        }

        public void CancelEdit()
        {
            if (!this.isEdit)
                return;
            isEdit = false;
            this.Id = backup.Id;
        }

        public void EndEdit()
        {
            if (this.isEdit == false)
                return;
            this.isEdit = false;
            this.backup = null;
        }

        #endregion
        private int _id;
        private string _name;
        private bool isEdit;
        private Kid backup;

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }

}
}

Xaml代码：

<Window x:Class="WpfApplication7.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<DockPanel LastChildFill="True" Margin="-1,5,1,-5">
    <Button Content="Add" Height="30" Click="Button_Click" DockPanel.Dock="Top"/>
    <DataGrid ItemsSource="{Binding Path=People}"
              AutoGenerateColumns="False"
              SelectionUnit="CellOrRowHeader"
              RowDetailsVisibilityMode="Visible">
        <DataGrid.Columns>
            <DataGridTextColumn Header="Salary" Binding="{Binding Path=Salary,StringFormat='{}{0:#,0}'}"/>
            <DataGridTextColumn Header="Name" Binding="{Binding Path=Name}"/>
            <DataGridCheckBoxColumn Header="IsLocked" Binding="{Binding Path=IsLocked,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
        </DataGrid.Columns>

        <DataGrid.RowDetailsTemplate>
            <DataTemplate>
                <DataGrid
                    ItemsSource="{Binding Path=Kids}"
              AutoGenerateColumns="False"
                    IsReadOnly="{Binding Path=IsLocked}"
              SelectionUnit="CellOrRowHeader">
                    <DataGrid.Columns>
                        <DataGridTextColumn Header="Id" Binding="{Binding Path=Id,StringFormat='{}{0:#,0}'}"/>
                        <DataGridTextColumn Header="Name" Binding="{Binding Path=Name}"/>
                    </DataGrid.Columns>
                </DataGrid>
            </DataTemplate>

        </DataGrid.RowDetailsTemplate>
    </DataGrid>
</DockPanel>

Answer 1

您可以将ID的类型从 int 更改为字符串

如果Id列为Unique，则必须将其设为 ReadOnly

或者你可以通过IvalueConverter处理它

关注此

创建一个类并实现IValueConverter

public class IntConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (value == null || value.ToString()=="")
            return 0;
        return value;
    }
}

然后将Coverter作为资源添加到您的Window

xmlns:local="clr-namespace:WpfApplication1"

和

<Window.Resources>
    <local:IntConverter x:Key="converter" />
</Window.Resources>

最后将转换器添加到 ID 列

<DataGridTextColumn Header="Id" Binding="{Binding Path=Id,StringFormat='{}{0:#,0}',Converter={StaticResource converter}}" />

Answer 2

尝试在Id列上设置TargetNullValue并使Kid.Id成为可以为空的int，然后你应该解决问题。

有关TargetNUllValue属性的信息，请参阅：http://msdn.microsoft.com/en-us/library/system.windows.data.bindingbase.targetnullvalue.aspx

代码背后：

public class Kid : IEditableObject, INotifyPropertyChanged
    {
        public int? Id
        {
            get { return _id; }
            set
            {
                this._id = value;
                if (PropertyChanged != null)
                    this.PropertyChanged(this, new PropertyChangedEventArgs("Id"));

            }

        }
        public string Name
        {
            get { return _name; }
            set
            {
                this._name = value;
                if (PropertyChanged != null)
                    this.PropertyChanged(this, new PropertyChangedEventArgs("Name"));

            }
        }
        public Person Parent { get; set; }

        public Kid()
        {
            this.Id = 12345;
            this.Name = "kidname";
        }

        public Kid(int? id, string name = "kidname")
        {
            this.Id = id;
            this.Name = name;
        }

        #region IEditableObject Members

        public void BeginEdit()
        {
            if (isEdit) return;
            isEdit = true;
            this.backup = this.MemberwiseClone() as Kid;
        }

        public void CancelEdit()
        {
            if (!this.isEdit)
                return;
            isEdit = false;
            this.Id = backup.Id;
        }

        public void EndEdit()
        {
            if (this.isEdit == false)
                return;
            this.isEdit = false;
            this.backup = null;
        }

        #endregion
        private int? _id;
        private string _name;
        private bool isEdit;
        private Kid backup;

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        #endregion
    }

WPF :(确保您已添加系统：引用

<Window x:Class="WpfApplication3.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:system="clr-namespace:System;assembly=mscorlib"
        Title="MainWindow" Height="350" Width="525">
    <DockPanel LastChildFill="True" Margin="-1,5,1,-5">
        <Button Content="Add" Height="30" Click="Button_Click" DockPanel.Dock="Top"/>
        <DataGrid ItemsSource="{Binding Path=People}"
              AutoGenerateColumns="False"
              SelectionUnit="CellOrRowHeader"
              RowDetailsVisibilityMode="Visible">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Salary" Binding="{Binding Path=Salary,StringFormat='{}{0:#,0}'}"/>
                <DataGridTextColumn Header="Name" Binding="{Binding Path=Name}"/>
                <DataGridCheckBoxColumn Header="IsLocked" Binding="{Binding Path=IsLocked,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
            </DataGrid.Columns>

            <DataGrid.RowDetailsTemplate>
                <DataTemplate>
                    <DataGrid
                    ItemsSource="{Binding Path=Kids}"
              AutoGenerateColumns="False"
                    IsReadOnly="{Binding Path=IsLocked}"
              SelectionUnit="CellOrRowHeader">
                        <DataGrid.Columns>
                            <DataGridTextColumn Header="Id" Binding="{Binding Path=Id,StringFormat='{}{0:#,0}', TargetNullValue={x:Static system:String.Empty}}"/>
                            <DataGridTextColumn  Header="Name" Binding="{Binding Path=Name}"/>
                        </DataGrid.Columns>
                    </DataGrid>
                </DataTemplate>

            </DataGrid.RowDetailsTemplate>
        </DataGrid>
    </DockPanel>
</Window>

Wpf datagrid在运行时将状态从只读状态更改为可编辑状态

2 个答案: